On the characteristics of peritectic Gd_2BaCuO_5 at the pro-peritectic stage with increasing amounts of external Gd_2BaCuO_5

摘要

The effect of different amounts of Gd_2BaCuO_5 (211) in the starting composition of Gd_2Ba_2CuO_3O_8-y (123) on the formation and refining behaviour of the 211 phase particles produced during the peritectic decomposition of 123 has been investigated. In the absence of any extra 211 in the liquid at the pro-peritectic stage, the morphology of the peritectically formed 211 particles is acicular with high aspect ratio; whereas, even small amounts of already existing 211, by acting as nucleating sites for the 211 generated by the decomposition of 123, change the morphology form acicular to circular. The average size of the 211 is found to decrease according to an inverse power law with respect to the number of nucleating centres. The change in morphology is discussed and a quantitative analysis of the average sizes of the 211 is presented.